/*
 * Copyright (c) 1994, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 */

package java.lang;

import java.io.ObjectStreamField;
import java.io.UnsupportedEncodingException;
import java.nio.charset.Charset;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.Formatter;
import java.util.Locale;
import java.util.Objects;
import java.util.StringJoiner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.regex.PatternSyntaxException;

/**
 * The {@code String} class represents character strings. All
 * string literals in Java programs, such as {@code "abc"}, are
 * implemented as instances of this class.
 * <p>
 * Strings are constant; their values cannot be changed after they
 * are created. String buffers support mutable strings.
 * Because String objects are immutable they can be shared. For example:
 * <blockquote><pre>
 *     String str = "abc";
 * </pre></blockquote><p>
 * is equivalent to:
 * <blockquote><pre>
 *     char data[] = {'a', 'b', 'c'};
 *     String str = new String(data);
 * </pre></blockquote><p>
 * Here are some more examples of how strings can be used:
 * <blockquote><pre>
 *     System.out.println("abc");
 *     String cde = "cde";
 *     System.out.println("abc" + cde);
 *     String c = "abc".substring(2,3);
 *     String d = cde.substring(1, 2);
 * </pre></blockquote>
 * <p>
 * The class {@code String} includes methods for examining
 * individual characters of the sequence, for comparing strings, for
 * searching strings, for extracting substrings, and for creating a
 * copy of a string with all characters translated to uppercase or to
 * lowercase. Case mapping is based on the Unicode Standard version
 * specified by the {@link java.lang.Character Character} class.
 * <p>
 * The Java language provides special support for the string
 * concatenation operator (&nbsp;+&nbsp;), and for conversion of
 * other objects to strings. String concatenation is implemented
 * through the {@code StringBuilder}(or {@code StringBuffer})
 * class and its {@code append} method.
 * String conversions are implemented through the method
 * {@code toString}, defined by {@code Object} and
 * inherited by all classes in Java. For additional information on
 * string concatenation and conversion, see Gosling, Joy, and Steele,
 * <i>The Java Language Specification</i>.
 *
 * <p> Unless otherwise noted, passing a <tt>null</tt> argument to a constructor
 * or method in this class will cause a {@link NullPointerException} to be
 * thrown.
 *
 * <p>A {@code String} represents a string in the UTF-16 format
 * in which <em>supplementary characters</em> are represented by <em>surrogate
 * pairs</em> (see the section <a href="Character.html#unicode">Unicode
 * Character Representations</a> in the {@code Character} class for
 * more information).
 * Index values refer to {@code char} code units, so a supplementary
 * character uses two positions in a {@code String}.
 * <p>The {@code String} class provides methods for dealing with
 * Unicode code points (i.e., characters), in addition to those for
 * dealing with Unicode code units (i.e., {@code char} values).
 *
 * @author Lee Boynton
 * @author Arthur van Hoff
 * @author Martin Buchholz
 * @author Ulf Zibis
 * @see java.lang.Object#toString()
 * @see java.lang.StringBuffer
 * @see java.lang.StringBuilder
 * @see java.nio.charset.Charset
 * @since JDK1.0
 */

public final class String
    implements java.io.Serializable, Comparable<String>, CharSequence {

  /**
   * The value is used for character storage.
   */
  private final char value[];

  /**
   * Cache the hash code for the string
   */
  private int hash; // Default to 0

  /**
   * use serialVersionUID from JDK 1.0.2 for interoperability
   */
  private static final long serialVersionUID = -6849794470754667710L;

  /**
   * Class String is special cased within the Serialization Stream Protocol.
   *
   * A String instance is written into an ObjectOutputStream according to
   * <a href="{@docRoot}/../platform/serialization/spec/output.html">
   * Object Serialization Specification, Section 6.2, "Stream Elements"</a>
   */
  private static final ObjectStreamField[] serialPersistentFields =
      new ObjectStreamField[0];

  /**
   * Initializes a newly created {@code String} object so that it represents
   * an empty character sequence.  Note that use of this constructor is
   * unnecessary since Strings are immutable.
   */
  public String() {
    this.value = "".value;
  }

  /**
   * Initializes a newly created {@code String} object so that it represents
   * the same sequence of characters as the argument; in other words, the
   * newly created string is a copy of the argument string. Unless an
   * explicit copy of {@code original} is needed, use of this constructor is
   * unnecessary since Strings are immutable.
   *
   * @param original A {@code String}
   */
  public String(String original) {
    this.value = original.value;
    this.hash = original.hash;
  }

  /**
   * Allocates a new {@code String} so that it represents the sequence of
   * characters currently contained in the character array argument. The
   * contents of the character array are copied; subsequent modification of
   * the character array does not affect the newly created string.
   *
   * @param value The initial value of the string
   */
  public String(char value[]) {
    this.value = Arrays.copyOf(value, value.length);
  }

  /**
   * Allocates a new {@code String} that contains characters from a subarray
   * of the character array argument. The {@code offset} argument is the
   * index of the first character of the subarray and the {@code count}
   * argument specifies the length of the subarray. The contents of the
   * subarray are copied; subsequent modification of the character array does
   * not affect the newly created string.
   *
   * @param value Array that is the source of characters
   * @param offset The initial offset
   * @param count The length
   * @throws IndexOutOfBoundsException If the {@code offset} and {@code count} arguments index
   * characters outside the bounds of the {@code value} array
   */
  public String(char value[], int offset, int count) {
    if (offset < 0) {
      throw new StringIndexOutOfBoundsException(offset);
    }
    if (count <= 0) {
      if (count < 0) {
        throw new StringIndexOutOfBoundsException(count);
      }
      if (offset <= value.length) {
        this.value = "".value;
        return;
      }
    }
    // Note: offset or count might be near -1>>>1.
    if (offset > value.length - count) {
      throw new StringIndexOutOfBoundsException(offset + count);
    }
    this.value = Arrays.copyOfRange(value, offset, offset + count);
  }

  /**
   * Allocates a new {@code String} that contains characters from a subarray
   * of the <a href="Character.html#unicode">Unicode code point</a> array
   * argument.  The {@code offset} argument is the index of the first code
   * point of the subarray and the {@code count} argument specifies the
   * length of the subarray.  The contents of the subarray are converted to
   * {@code char}s; subsequent modification of the {@code int} array does not
   * affect the newly created string.
   *
   * @param codePoints Array that is the source of Unicode code points
   * @param offset The initial offset
   * @param count The length
   * @throws IllegalArgumentException If any invalid Unicode code point is found in {@code
   * codePoints}
   * @throws IndexOutOfBoundsException If the {@code offset} and {@code count} arguments index
   * characters outside the bounds of the {@code codePoints} array
   * @since 1.5
   */
  public String(int[] codePoints, int offset, int count) {
    if (offset < 0) {
      throw new StringIndexOutOfBoundsException(offset);
    }
    if (count <= 0) {
      if (count < 0) {
        throw new StringIndexOutOfBoundsException(count);
      }
      if (offset <= codePoints.length) {
        this.value = "".value;
        return;
      }
    }
    // Note: offset or count might be near -1>>>1.
    if (offset > codePoints.length - count) {
      throw new StringIndexOutOfBoundsException(offset + count);
    }

    final int end = offset + count;

    // Pass 1: Compute precise size of char[]
    int n = count;
    for (int i = offset; i < end; i++) {
      int c = codePoints[i];
      if (Character.isBmpCodePoint(c)) {
        continue;
      } else if (Character.isValidCodePoint(c)) {
        n++;
      } else {
        throw new IllegalArgumentException(Integer.toString(c));
      }
    }

    // Pass 2: Allocate and fill in char[]
    final char[] v = new char[n];

    for (int i = offset, j = 0; i < end; i++, j++) {
      int c = codePoints[i];
      if (Character.isBmpCodePoint(c)) {
        v[j] = (char) c;
      } else {
        Character.toSurrogates(c, v, j++);
      }
    }

    this.value = v;
  }

  /**
   * Allocates a new {@code String} constructed from a subarray of an array
   * of 8-bit integer values.
   *
   * <p> The {@code offset} argument is the index of the first byte of the
   * subarray, and the {@code count} argument specifies the length of the
   * subarray.
   *
   * <p> Each {@code byte} in the subarray is converted to a {@code char} as
   * specified in the method above.
   *
   * @param ascii The bytes to be converted to characters
   * @param hibyte The top 8 bits of each 16-bit Unicode code unit
   * @param offset The initial offset
   * @param count The length
   * @throws IndexOutOfBoundsException If the {@code offset} or {@code count} argument is invalid
   * @see #String(byte[], int)
   * @see #String(byte[], int, int, java.lang.String)
   * @see #String(byte[], int, int, java.nio.charset.Charset)
   * @see #String(byte[], int, int)
   * @see #String(byte[], java.lang.String)
   * @see #String(byte[], java.nio.charset.Charset)
   * @see #String(byte[])
   * @deprecated This method does not properly convert bytes into characters. As of JDK&nbsp;1.1,
   * the preferred way to do this is via the {@code String} constructors that take a {@link
   * java.nio.charset.Charset}, charset name, or that use the platform's default charset.
   */
  @Deprecated
  public String(byte ascii[], int hibyte, int offset, int count) {
    checkBounds(ascii, offset, count);
    char value[] = new char[count];

    if (hibyte == 0) {
      for (int i = count; i-- > 0; ) {
        value[i] = (char) (ascii[i + offset] & 0xff);
      }
    } else {
      hibyte <<= 8;
      for (int i = count; i-- > 0; ) {
        value[i] = (char) (hibyte | (ascii[i + offset] & 0xff));
      }
    }
    this.value = value;
  }

  /**
   * Allocates a new {@code String} containing characters constructed from
   * an array of 8-bit integer values. Each character <i>c</i>in the
   * resulting string is constructed from the corresponding component
   * <i>b</i> in the byte array such that:
   *
   * <blockquote><pre>
   *     <b><i>c</i></b> == (char)(((hibyte &amp; 0xff) &lt;&lt; 8)
   *                         | (<b><i>b</i></b> &amp; 0xff))
   * </pre></blockquote>
   *
   * @param ascii The bytes to be converted to characters
   * @param hibyte The top 8 bits of each 16-bit Unicode code unit
   * @see #String(byte[], int, int, java.lang.String)
   * @see #String(byte[], int, int, java.nio.charset.Charset)
   * @see #String(byte[], int, int)
   * @see #String(byte[], java.lang.String)
   * @see #String(byte[], java.nio.charset.Charset)
   * @see #String(byte[])
   * @deprecated This method does not properly convert bytes into characters.  As of JDK&nbsp;1.1,
   * the preferred way to do this is via the {@code String} constructors that take a {@link
   * java.nio.charset.Charset}, charset name, or that use the platform's default charset.
   */
  @Deprecated
  public String(byte ascii[], int hibyte) {
    this(ascii, hibyte, 0, ascii.length);
  }

  /* Common private utility method used to bounds check the byte array
   * and requested offset & length values used by the String(byte[],..)
   * constructors.
   */
  private static void checkBounds(byte[] bytes, int offset, int length) {
    if (length < 0) {
      throw new StringIndexOutOfBoundsException(length);
    }
    if (offset < 0) {
      throw new StringIndexOutOfBoundsException(offset);
    }
    if (offset > bytes.length - length) {
      throw new StringIndexOutOfBoundsException(offset + length);
    }
  }

  /**
   * Constructs a new {@code String} by decoding the specified subarray of
   * bytes using the specified charset.  The length of the new {@code String}
   * is a function of the charset, and hence may not be equal to the length
   * of the subarray.
   *
   * <p> The behavior of this constructor when the given bytes are not valid
   * in the given charset is unspecified.  The {@link
   * java.nio.charset.CharsetDecoder} class should be used when more control
   * over the decoding process is required.
   *
   * @param bytes The bytes to be decoded into characters
   * @param offset The index of the first byte to decode
   * @param length The number of bytes to decode
   * @param charsetName The name of a supported {@linkplain java.nio.charset.Charset charset}
   * @throws UnsupportedEncodingException If the named charset is not supported
   * @throws IndexOutOfBoundsException If the {@code offset} and {@code length} arguments index
   * characters outside the bounds of the {@code bytes} array
   * @since JDK1.1
   */
  public String(byte bytes[], int offset, int length, String charsetName)
      throws UnsupportedEncodingException {
    if (charsetName == null) {
      throw new NullPointerException("charsetName");
    }
    checkBounds(bytes, offset, length);
    this.value = StringCoding.decode(charsetName, bytes, offset, length);
  }

  /**
   * Constructs a new {@code String} by decoding the specified subarray of
   * bytes using the specified {@linkplain java.nio.charset.Charset charset}.
   * The length of the new {@code String} is a function of the charset, and
   * hence may not be equal to the length of the subarray.
   *
   * <p> This method always replaces malformed-input and unmappable-character
   * sequences with this charset's default replacement string.  The {@link
   * java.nio.charset.CharsetDecoder} class should be used when more control
   * over the decoding process is required.
   *
   * @param bytes The bytes to be decoded into characters
   * @param offset The index of the first byte to decode
   * @param length The number of bytes to decode
   * @param charset The {@linkplain java.nio.charset.Charset charset} to be used to decode the
   * {@code bytes}
   * @throws IndexOutOfBoundsException If the {@code offset} and {@code length} arguments index
   * characters outside the bounds of the {@code bytes} array
   * @since 1.6
   */
  public String(byte bytes[], int offset, int length, Charset charset) {
    if (charset == null) {
      throw new NullPointerException("charset");
    }
    checkBounds(bytes, offset, length);
    this.value = StringCoding.decode(charset, bytes, offset, length);
  }

  /**
   * Constructs a new {@code String} by decoding the specified array of bytes
   * using the specified {@linkplain java.nio.charset.Charset charset}.  The
   * length of the new {@code String} is a function of the charset, and hence
   * may not be equal to the length of the byte array.
   *
   * <p> The behavior of this constructor when the given bytes are not valid
   * in the given charset is unspecified.  The {@link
   * java.nio.charset.CharsetDecoder} class should be used when more control
   * over the decoding process is required.
   *
   * @param bytes The bytes to be decoded into characters
   * @param charsetName The name of a supported {@linkplain java.nio.charset.Charset charset}
   * @throws UnsupportedEncodingException If the named charset is not supported
   * @since JDK1.1
   */
  public String(byte bytes[], String charsetName)
      throws UnsupportedEncodingException {
    this(bytes, 0, bytes.length, charsetName);
  }

  /**
   * Constructs a new {@code String} by decoding the specified array of
   * bytes using the specified {@linkplain java.nio.charset.Charset charset}.
   * The length of the new {@code String} is a function of the charset, and
   * hence may not be equal to the length of the byte array.
   *
   * <p> This method always replaces malformed-input and unmappable-character
   * sequences with this charset's default replacement string.  The {@link
   * java.nio.charset.CharsetDecoder} class should be used when more control
   * over the decoding process is required.
   *
   * @param bytes The bytes to be decoded into characters
   * @param charset The {@linkplain java.nio.charset.Charset charset} to be used to decode the
   * {@code bytes}
   * @since 1.6
   */
  public String(byte bytes[], Charset charset) {
    this(bytes, 0, bytes.length, charset);
  }

  /**
   * Constructs a new {@code String} by decoding the specified subarray of
   * bytes using the platform's default charset.  The length of the new
   * {@code String} is a function of the charset, and hence may not be equal
   * to the length of the subarray.
   *
   * <p> The behavior of this constructor when the given bytes are not valid
   * in the default charset is unspecified.  The {@link
   * java.nio.charset.CharsetDecoder} class should be used when more control
   * over the decoding process is required.
   *
   * @param bytes The bytes to be decoded into characters
   * @param offset The index of the first byte to decode
   * @param length The number of bytes to decode
   * @throws IndexOutOfBoundsException If the {@code offset} and the {@code length} arguments index
   * characters outside the bounds of the {@code bytes} array
   * @since JDK1.1
   */
  public String(byte bytes[], int offset, int length) {
    checkBounds(bytes, offset, length);
    this.value = StringCoding.decode(bytes, offset, length);
  }

  /**
   * Constructs a new {@code String} by decoding the specified array of bytes
   * using the platform's default charset.  The length of the new {@code
   * String} is a function of the charset, and hence may not be equal to the
   * length of the byte array.
   *
   * <p> The behavior of this constructor when the given bytes are not valid
   * in the default charset is unspecified.  The {@link
   * java.nio.charset.CharsetDecoder} class should be used when more control
   * over the decoding process is required.
   *
   * @param bytes The bytes to be decoded into characters
   * @since JDK1.1
   */
  public String(byte bytes[]) {
    this(bytes, 0, bytes.length);
  }

  /**
   * Allocates a new string that contains the sequence of characters
   * currently contained in the string buffer argument. The contents of the
   * string buffer are copied; subsequent modification of the string buffer
   * does not affect the newly created string.
   *
   * @param buffer A {@code StringBuffer}
   */
  public String(StringBuffer buffer) {
    synchronized (buffer) {
      this.value = Arrays.copyOf(buffer.getValue(), buffer.length());
    }
  }

  /**
   * Allocates a new string that contains the sequence of characters
   * currently contained in the string builder argument. The contents of the
   * string builder are copied; subsequent modification of the string builder
   * does not affect the newly created string.
   *
   * <p> This constructor is provided to ease migration to {@code
   * StringBuilder}. Obtaining a string from a string builder via the {@code
   * toString} method is likely to run faster and is generally preferred.
   *
   * @param builder A {@code StringBuilder}
   * @since 1.5
   */
  public String(StringBuilder builder) {
    this.value = Arrays.copyOf(builder.getValue(), builder.length());
  }

  /*
  * Package private constructor which shares value array for speed.
  * this constructor is always expected to be called with share==true.
  * a separate constructor is needed because we already have a public
  * String(char[]) constructor that makes a copy of the given char[].
  */
  String(char[] value, boolean share) {
    // assert share : "unshared not supported";
    this.value = value;
  }

  /**
   * Returns the length of this string.
   * The length is equal to the number of <a href="Character.html#unicode">Unicode
   * code units</a> in the string.
   *
   * @return the length of the sequence of characters represented by this object.
   */
  public int length() {
    return value.length;
  }

  /**
   * Returns {@code true} if, and only if, {@link #length()} is {@code 0}.
   *
   * @return {@code true} if {@link #length()} is {@code 0}, otherwise {@code false}
   * @since 1.6
   */
  public boolean isEmpty() {
    return value.length == 0;
  }

  /**
   * Returns the {@code char} value at the
   * specified index. An index ranges from {@code 0} to
   * {@code length() - 1}. The first {@code char} value of the sequence
   * is at index {@code 0}, the next at index {@code 1},
   * and so on, as for array indexing.
   *
   * <p>If the {@code char} value specified by the index is a
   * <a href="Character.html#unicode">surrogate</a>, the surrogate
   * value is returned.
   *
   * @param index the index of the {@code char} value.
   * @return the {@code char} value at the specified index of this string. The first {@code char}
   * value is at index {@code 0}.
   * @throws IndexOutOfBoundsException if the {@code index} argument is negative or not less than
   * the length of this string.
   */
  public char charAt(int index) {
    if ((index < 0) || (index >= value.length)) {
      throw new StringIndexOutOfBoundsException(index);
    }
    return value[index];
  }

  /**
   * Returns the character (Unicode code point) at the specified
   * index. The index refers to {@code char} values
   * (Unicode code units) and ranges from {@code 0} to
   * {@link #length()}{@code  - 1}.
   *
   * <p> If the {@code char} value specified at the given index
   * is in the high-surrogate range, the following index is less
   * than the length of this {@code String}, and the
   * {@code char} value at the following index is in the
   * low-surrogate range, then the supplementary code point
   * corresponding to this surrogate pair is returned. Otherwise,
   * the {@code char} value at the given index is returned.
   *
   * @param index the index to the {@code char} values
   * @return the code point value of the character at the {@code index}
   * @throws IndexOutOfBoundsException if the {@code index} argument is negative or not less than
   * the length of this string.
   * @since 1.5
   */
  public int codePointAt(int index) {
    if ((index < 0) || (index >= value.length)) {
      throw new StringIndexOutOfBoundsException(index);
    }
    return Character.codePointAtImpl(value, index, value.length);
  }

  /**
   * Returns the character (Unicode code point) before the specified
   * index. The index refers to {@code char} values
   * (Unicode code units) and ranges from {@code 1} to {@link
   * CharSequence#length() length}.
   *
   * <p> If the {@code char} value at {@code (index - 1)}
   * is in the low-surrogate range, {@code (index - 2)} is not
   * negative, and the {@code char} value at {@code (index -
   * 2)} is in the high-surrogate range, then the
   * supplementary code point value of the surrogate pair is
   * returned. If the {@code char} value at {@code index -
   * 1} is an unpaired low-surrogate or a high-surrogate, the
   * surrogate value is returned.
   *
   * @param index the index following the code point that should be returned
   * @return the Unicode code point value before the given index.
   * @throws IndexOutOfBoundsException if the {@code index} argument is less than 1 or greater than
   * the length of this string.
   * @since 1.5
   */
  public int codePointBefore(int index) {
    int i = index - 1;
    if ((i < 0) || (i >= value.length)) {
      throw new StringIndexOutOfBoundsException(index);
    }
    return Character.codePointBeforeImpl(value, index, 0);
  }

  /**
   * Returns the number of Unicode code points in the specified text
   * range of this {@code String}. The text range begins at the
   * specified {@code beginIndex} and extends to the
   * {@code char} at index {@code endIndex - 1}. Thus the
   * length (in {@code char}s) of the text range is
   * {@code endIndex-beginIndex}. Unpaired surrogates within
   * the text range count as one code point each.
   *
   * @param beginIndex the index to the first {@code char} of the text range.
   * @param endIndex the index after the last {@code char} of the text range.
   * @return the number of Unicode code points in the specified text range
   * @throws IndexOutOfBoundsException if the {@code beginIndex} is negative, or {@code endIndex} is
   * larger than the length of this {@code String}, or {@code beginIndex} is larger than {@code
   * endIndex}.
   * @since 1.5
   */
  public int codePointCount(int beginIndex, int endIndex) {
    if (beginIndex < 0 || endIndex > value.length || beginIndex > endIndex) {
      throw new IndexOutOfBoundsException();
    }
    return Character.codePointCountImpl(value, beginIndex, endIndex - beginIndex);
  }

  /**
   * Returns the index within this {@code String} that is
   * offset from the given {@code index} by
   * {@code codePointOffset} code points. Unpaired surrogates
   * within the text range given by {@code index} and
   * {@code codePointOffset} count as one code point each.
   *
   * @param index the index to be offset
   * @param codePointOffset the offset in code points
   * @return the index within this {@code String}
   * @throws IndexOutOfBoundsException if {@code index} is negative or larger then the length of
   * this {@code String}, or if {@code codePointOffset} is positive and the substring starting with
   * {@code index} has fewer than {@code codePointOffset} code points, or if {@code codePointOffset}
   * is negative and the substring before {@code index} has fewer than the absolute value of {@code
   * codePointOffset} code points.
   * @since 1.5
   */
  public int offsetByCodePoints(int index, int codePointOffset) {
    if (index < 0 || index > value.length) {
      throw new IndexOutOfBoundsException();
    }
    return Character.offsetByCodePointsImpl(value, 0, value.length,
        index, codePointOffset);
  }

  /**
   * Copy characters from this string into dst starting at dstBegin.
   * This method doesn't perform any range checking.
   */
  void getChars(char dst[], int dstBegin) {
    System.arraycopy(value, 0, dst, dstBegin, value.length);
  }

  /**
   * Copies characters from this string into the destination character
   * array.
   * <p>
   * The first character to be copied is at index {@code srcBegin};
   * the last character to be copied is at index {@code srcEnd-1}
   * (thus the total number of characters to be copied is
   * {@code srcEnd-srcBegin}). The characters are copied into the
   * subarray of {@code dst} starting at index {@code dstBegin}
   * and ending at index:
   * <blockquote><pre>
   *     dstBegin + (srcEnd-srcBegin) - 1
   * </pre></blockquote>
   *
   * @param srcBegin index of the first character in the string to copy.
   * @param srcEnd index after the last character in the string to copy.
   * @param dst the destination array.
   * @param dstBegin the start offset in the destination array.
   * @throws IndexOutOfBoundsException If any of the following is true: <ul><li>{@code srcBegin} is
   * negative. <li>{@code srcBegin} is greater than {@code srcEnd} <li>{@code srcEnd} is greater
   * than the length of this string <li>{@code dstBegin} is negative <li>{@code
   * dstBegin+(srcEnd-srcBegin)} is larger than {@code dst.length}</ul>
   */
  public void getChars(int srcBegin, int srcEnd, char dst[], int dstBegin) {
    if (srcBegin < 0) {
      throw new StringIndexOutOfBoundsException(srcBegin);
    }
    if (srcEnd > value.length) {
      throw new StringIndexOutOfBoundsException(srcEnd);
    }
    if (srcBegin > srcEnd) {
      throw new StringIndexOutOfBoundsException(srcEnd - srcBegin);
    }
    System.arraycopy(value, srcBegin, dst, dstBegin, srcEnd - srcBegin);
  }

  /**
   * Copies characters from this string into the destination byte array. Each
   * byte receives the 8 low-order bits of the corresponding character. The
   * eight high-order bits of each character are not copied and do not
   * participate in the transfer in any way.
   *
   * <p> The first character to be copied is at index {@code srcBegin}; the
   * last character to be copied is at index {@code srcEnd-1}.  The total
   * number of characters to be copied is {@code srcEnd-srcBegin}. The
   * characters, converted to bytes, are copied into the subarray of {@code
   * dst} starting at index {@code dstBegin} and ending at index:
   *
   * <blockquote><pre>
   *     dstBegin + (srcEnd-srcBegin) - 1
   * </pre></blockquote>
   *
   * @param srcBegin Index of the first character in the string to copy
   * @param srcEnd Index after the last character in the string to copy
   * @param dst The destination array
   * @param dstBegin The start offset in the destination array
   * @throws IndexOutOfBoundsException If any of the following is true: <ul> <li> {@code srcBegin}
   * is negative <li> {@code srcBegin} is greater than {@code srcEnd} <li> {@code srcEnd} is greater
   * than the length of this String <li> {@code dstBegin} is negative <li> {@code
   * dstBegin+(srcEnd-srcBegin)} is larger than {@code dst.length} </ul>
   * @deprecated This method does not properly convert characters into bytes.  As of JDK&nbsp;1.1,
   * the preferred way to do this is via the {@link #getBytes()} method, which uses the platform's
   * default charset.
   */
  @Deprecated
  public void getBytes(int srcBegin, int srcEnd, byte dst[], int dstBegin) {
    if (srcBegin < 0) {
      throw new StringIndexOutOfBoundsException(srcBegin);
    }
    if (srcEnd > value.length) {
      throw new StringIndexOutOfBoundsException(srcEnd);
    }
    if (srcBegin > srcEnd) {
      throw new StringIndexOutOfBoundsException(srcEnd - srcBegin);
    }
    Objects.requireNonNull(dst);

    int j = dstBegin;
    int n = srcEnd;
    int i = srcBegin;
    char[] val = value;   /* avoid getfield opcode */

    while (i < n) {
      dst[j++] = (byte) val[i++];
    }
  }

  /**
   * Encodes this {@code String} into a sequence of bytes using the named
   * charset, storing the result into a new byte array.
   *
   * <p> The behavior of this method when this string cannot be encoded in
   * the given charset is unspecified.  The {@link
   * java.nio.charset.CharsetEncoder} class should be used when more control
   * over the encoding process is required.
   *
   * @param charsetName The name of a supported {@linkplain java.nio.charset.Charset charset}
   * @return The resultant byte array
   * @throws UnsupportedEncodingException If the named charset is not supported
   * @since JDK1.1
   */
  public byte[] getBytes(String charsetName)
      throws UnsupportedEncodingException {
    if (charsetName == null) {
      throw new NullPointerException();
    }
    return StringCoding.encode(charsetName, value, 0, value.length);
  }

  /**
   * Encodes this {@code String} into a sequence of bytes using the given
   * {@linkplain java.nio.charset.Charset charset}, storing the result into a
   * new byte array.
   *
   * <p> This method always replaces malformed-input and unmappable-character
   * sequences with this charset's default replacement byte array.  The
   * {@link java.nio.charset.CharsetEncoder} class should be used when more
   * control over the encoding process is required.
   *
   * @param charset The {@linkplain java.nio.charset.Charset} to be used to encode the {@code
   * String}
   * @return The resultant byte array
   * @since 1.6
   */
  public byte[] getBytes(Charset charset) {
    if (charset == null) {
      throw new NullPointerException();
    }
    return StringCoding.encode(charset, value, 0, value.length);
  }

  /**
   * Encodes this {@code String} into a sequence of bytes using the
   * platform's default charset, storing the result into a new byte array.
   *
   * <p> The behavior of this method when this string cannot be encoded in
   * the default charset is unspecified.  The {@link
   * java.nio.charset.CharsetEncoder} class should be used when more control
   * over the encoding process is required.
   *
   * @return The resultant byte array
   * @since JDK1.1
   */
  public byte[] getBytes() {
    return StringCoding.encode(value, 0, value.length);
  }

  /**
   * Compares this string to the specified object.  The result is {@code
   * true} if and only if the argument is not {@code null} and is a {@code
   * String} object that represents the same sequence of characters as this
   * object.
   *
   * @param anObject The object to compare this {@code String} against
   * @return {@code true} if the given object represents a {@code String} equivalent to this string,
   * {@code false} otherwise
   * @see #compareTo(String)
   * @see #equalsIgnoreCase(String)
   */
  public boolean equals(Object anObject) {
    if (this == anObject) {
      return true;
    }
    if (anObject instanceof String) {
      String anotherString = (String) anObject;
      int n = value.length;
      if (n == anotherString.value.length) {
        char v1[] = value;
        char v2[] = anotherString.value;
        int i = 0;
        while (n-- != 0) {
          if (v1[i] != v2[i]) {
            return false;
          }
          i++;
        }
        return true;
      }
    }
    return false;
  }

  /**
   * Compares this string to the specified {@code StringBuffer}.  The result
   * is {@code true} if and only if this {@code String} represents the same
   * sequence of characters as the specified {@code StringBuffer}. This method
   * synchronizes on the {@code StringBuffer}.
   *
   * @param sb The {@code StringBuffer} to compare this {@code String} against
   * @return {@code true} if this {@code String} represents the same sequence of characters as the
   * specified {@code StringBuffer}, {@code false} otherwise
   * @since 1.4
   */
  public boolean contentEquals(StringBuffer sb) {
    return contentEquals((CharSequence) sb);
  }

  private boolean nonSyncContentEquals(AbstractStringBuilder sb) {
    char v1[] = value;
    char v2[] = sb.getValue();
    int n = v1.length;
    if (n != sb.length()) {
      return false;
    }
    for (int i = 0; i < n; i++) {
      if (v1[i] != v2[i]) {
        return false;
      }
    }
    return true;
  }

  /**
   * Compares this string to the specified {@code CharSequence}.  The
   * result is {@code true} if and only if this {@code String} represents the
   * same sequence of char values as the specified sequence. Note that if the
   * {@code CharSequence} is a {@code StringBuffer} then the method
   * synchronizes on it.
   *
   * @param cs The sequence to compare this {@code String} against
   * @return {@code true} if this {@code String} represents the same sequence of char values as the
   * specified sequence, {@code false} otherwise
   * @since 1.5
   */
  public boolean contentEquals(CharSequence cs) {
    // Argument is a StringBuffer, StringBuilder
    if (cs instanceof AbstractStringBuilder) {
      if (cs instanceof StringBuffer) {
        synchronized (cs) {
          return nonSyncContentEquals((AbstractStringBuilder) cs);
        }
      } else {
        return nonSyncContentEquals((AbstractStringBuilder) cs);
      }
    }
    // Argument is a String
    if (cs instanceof String) {
      return equals(cs);
    }
    // Argument is a generic CharSequence
    char v1[] = value;
    int n = v1.length;
    if (n != cs.length()) {
      return false;
    }
    for (int i = 0; i < n; i++) {
      if (v1[i] != cs.charAt(i)) {
        return false;
      }
    }
    return true;
  }

  /**
   * Compares this {@code String} to another {@code String}, ignoring case
   * considerations.  Two strings are considered equal ignoring case if they
   * are of the same length and corresponding characters in the two strings
   * are equal ignoring case.
   *
   * <p> Two characters {@code c1} and {@code c2} are considered the same
   * ignoring case if at least one of the following is true:
   * <ul>
   * <li> The two characters are the same (as compared by the
   * {@code ==} operator)
   * <li> Applying the method {@link
   * java.lang.Character#toUpperCase(char)} to each character
   * produces the same result
   * <li> Applying the method {@link
   * java.lang.Character#toLowerCase(char)} to each character
   * produces the same result
   * </ul>
   *
   * @param anotherString The {@code String} to compare this {@code String} against
   * @return {@code true} if the argument is not {@code null} and it represents an equivalent {@code
   * String} ignoring case; {@code false} otherwise
   * @see #equals(Object)
   */
  public boolean equalsIgnoreCase(String anotherString) {
    return (this == anotherString) ? true
        : (anotherString != null)
            && (anotherString.value.length == value.length)
            && regionMatches(true, 0, anotherString, 0, value.length);
  }

  /**
   * Compares two strings lexicographically.
   * The comparison is based on the Unicode value of each character in
   * the strings. The character sequence represented by this
   * {@code String} object is compared lexicographically to the
   * character sequence represented by the argument string. The result is
   * a negative integer if this {@code String} object
   * lexicographically precedes the argument string. The result is a
   * positive integer if this {@code String} object lexicographically
   * follows the argument string. The result is zero if the strings
   * are equal; {@code compareTo} returns {@code 0} exactly when
   * the {@link #equals(Object)} method would return {@code true}.
   * <p>
   * This is the definition of lexicographic ordering. If two strings are
   * different, then either they have different characters at some index
   * that is a valid index for both strings, or their lengths are different,
   * or both. If they have different characters at one or more index
   * positions, let <i>k</i> be the smallest such index; then the string
   * whose character at position <i>k</i> has the smaller value, as
   * determined by using the &lt; operator, lexicographically precedes the
   * other string. In this case, {@code compareTo} returns the
   * difference of the two character values at position {@code k} in
   * the two string -- that is, the value:
   * <blockquote><pre>
   * this.charAt(k)-anotherString.charAt(k)
   * </pre></blockquote>
   * If there is no index position at which they differ, then the shorter
   * string lexicographically precedes the longer string. In this case,
   * {@code compareTo} returns the difference of the lengths of the
   * strings -- that is, the value:
   * <blockquote><pre>
   * this.length()-anotherString.length()
   * </pre></blockquote>
   *
   * @param anotherString the {@code String} to be compared.
   * @return the value {@code 0} if the argument string is equal to this string; a value less than
   * {@code 0} if this string is lexicographically less than the string argument; and a value
   * greater than {@code 0} if this string is lexicographically greater than the string argument.
   */
  public int compareTo(String anotherString) {
    int len1 = value.length;
    int len2 = anotherString.value.length;
    int lim = Math.min(len1, len2);
    char v1[] = value;
    char v2[] = anotherString.value;

    int k = 0;
    while (k < lim) {
      char c1 = v1[k];
      char c2 = v2[k];
      if (c1 != c2) {
        return c1 - c2;
      }
      k++;
    }
    return len1 - len2;
  }

  /**
   * A Comparator that orders {@code String} objects as by
   * {@code compareToIgnoreCase}. This comparator is serializable.
   * <p>
   * Note that this Comparator does <em>not</em> take locale into account,
   * and will result in an unsatisfactory ordering for certain locales.
   * The java.text package provides <em>Collators</em> to allow
   * locale-sensitive ordering.
   *
   * @see java.text.Collator#compare(String, String)
   * @since 1.2
   */
  public static final Comparator<String> CASE_INSENSITIVE_ORDER
      = new CaseInsensitiveComparator();

  private static class CaseInsensitiveComparator
      implements Comparator<String>, java.io.Serializable {

    // use serialVersionUID from JDK 1.2.2 for interoperability
    private static final long serialVersionUID = 8575799808933029326L;

    public int compare(String s1, String s2) {
      int n1 = s1.length();
      int n2 = s2.length();
      int min = Math.min(n1, n2);
      for (int i = 0; i < min; i++) {
        char c1 = s1.charAt(i);
        char c2 = s2.charAt(i);
        if (c1 != c2) {
          c1 = Character.toUpperCase(c1);
          c2 = Character.toUpperCase(c2);
          if (c1 != c2) {
            c1 = Character.toLowerCase(c1);
            c2 = Character.toLowerCase(c2);
            if (c1 != c2) {
              // No overflow because of numeric promotion
              return c1 - c2;
            }
          }
        }
      }
      return n1 - n2;
    }

    /**
     * Replaces the de-serialized object.
     */
    private Object readResolve() {
      return CASE_INSENSITIVE_ORDER;
    }
  }

  /**
   * Compares two strings lexicographically, ignoring case
   * differences. This method returns an integer whose sign is that of
   * calling {@code compareTo} with normalized versions of the strings
   * where case differences have been eliminated by calling
   * {@code Character.toLowerCase(Character.toUpperCase(character))} on
   * each character.
   * <p>
   * Note that this method does <em>not</em> take locale into account,
   * and will result in an unsatisfactory ordering for certain locales.
   * The java.text package provides <em>collators</em> to allow
   * locale-sensitive ordering.
   *
   * @param str the {@code String} to be compared.
   * @return a negative integer, zero, or a positive integer as the specified String is greater
   * than, equal to, or less than this String, ignoring case considerations.
   * @see java.text.Collator#compare(String, String)
   * @since 1.2
   */
  public int compareToIgnoreCase(String str) {
    return CASE_INSENSITIVE_ORDER.compare(this, str);
  }

  /**
   * Tests if two string regions are equal.
   * <p>
   * A substring of this {@code String} object is compared to a substring
   * of the argument other. The result is true if these substrings
   * represent identical character sequences. The substring of this
   * {@code String} object to be compared begins at index {@code toffset}
   * and has length {@code len}. The substring of other to be compared
   * begins at index {@code ooffset} and has length {@code len}. The
   * result is {@code false} if and only if at least one of the following
   * is true:
   * <ul><li>{@code toffset} is negative.
   * <li>{@code ooffset} is negative.
   * <li>{@code toffset+len} is greater than the length of this
   * {@code String} object.
   * <li>{@code ooffset+len} is greater than the length of the other
   * argument.
   * <li>There is some nonnegative integer <i>k</i> less than {@code len}
   * such that:
   * {@code this.charAt(toffset + }<i>k</i>{@code ) != other.charAt(ooffset + }
   * <i>k</i>{@code )}
   * </ul>
   *
   * @param toffset the starting offset of the subregion in this string.
   * @param other the string argument.
   * @param ooffset the starting offset of the subregion in the string argument.
   * @param len the number of characters to compare.
   * @return {@code true} if the specified subregion of this string exactly matches the specified
   * subregion of the string argument; {@code false} otherwise.
   */
  public boolean regionMatches(int toffset, String other, int ooffset,
      int len) {
    char ta[] = value;
    int to = toffset;
    char pa[] = other.value;
    int po = ooffset;
    // Note: toffset, ooffset, or len might be near -1>>>1.
    if ((ooffset < 0) || (toffset < 0)
        || (toffset > (long) value.length - len)
        || (ooffset > (long) other.value.length - len)) {
      return false;
    }
    while (len-- > 0) {
      if (ta[to++] != pa[po++]) {
        return false;
      }
    }
    return true;
  }

  /**
   * Tests if two string regions are equal.
   * <p>
   * A substring of this {@code String} object is compared to a substring
   * of the argument {@code other}. The result is {@code true} if these
   * substrings represent character sequences that are the same, ignoring
   * case if and only if {@code ignoreCase} is true. The substring of
   * this {@code String} object to be compared begins at index
   * {@code toffset} and has length {@code len}. The substring of
   * {@code other} to be compared begins at index {@code ooffset} and
   * has length {@code len}. The result is {@code false} if and only if
   * at least one of the following is true:
   * <ul><li>{@code toffset} is negative.
   * <li>{@code ooffset} is negative.
   * <li>{@code toffset+len} is greater than the length of this
   * {@code String} object.
   * <li>{@code ooffset+len} is greater than the length of the other
   * argument.
   * <li>{@code ignoreCase} is {@code false} and there is some nonnegative
   * integer <i>k</i> less than {@code len} such that:
   * <blockquote><pre>
   * this.charAt(toffset+k) != other.charAt(ooffset+k)
   * </pre></blockquote>
   * <li>{@code ignoreCase} is {@code true} and there is some nonnegative
   * integer <i>k</i> less than {@code len} such that:
   * <blockquote><pre>
   * Character.toLowerCase(this.charAt(toffset+k)) !=
   * Character.toLowerCase(other.charAt(ooffset+k))
   * </pre></blockquote>
   * and:
   * <blockquote><pre>
   * Character.toUpperCase(this.charAt(toffset+k)) !=
   *         Character.toUpperCase(other.charAt(ooffset+k))
   * </pre></blockquote>
   * </ul>
   *
   * @param ignoreCase if {@code true}, ignore case when comparing characters.
   * @param toffset the starting offset of the subregion in this string.
   * @param other the string argument.
   * @param ooffset the starting offset of the subregion in the string argument.
   * @param len the number of characters to compare.
   * @return {@code true} if the specified subregion of this string matches the specified subregion
   * of the string argument; {@code false} otherwise. Whether the matching is exact or case
   * insensitive depends on the {@code ignoreCase} argument.
   */
  public boolean regionMatches(boolean ignoreCase, int toffset,
      String other, int ooffset, int len) {
    char ta[] = value;
    int to = toffset;
    char pa[] = other.value;
    int po = ooffset;
    // Note: toffset, ooffset, or len might be near -1>>>1.
    if ((ooffset < 0) || (toffset < 0)
        || (toffset > (long) value.length - len)
        || (ooffset > (long) other.value.length - len)) {
      return false;
    }
    while (len-- > 0) {
      char c1 = ta[to++];
      char c2 = pa[po++];
      if (c1 == c2) {
        continue;
      }
      if (ignoreCase) {
        // If characters don't match but case may be ignored,
        // try converting both characters to uppercase.
        // If the results match, then the comparison scan should
        // continue.
        char u1 = Character.toUpperCase(c1);
        char u2 = Character.toUpperCase(c2);
        if (u1 == u2) {
          continue;
        }
        // Unfortunately, conversion to uppercase does not work properly
        // for the Georgian alphabet, which has strange rules about case
        // conversion.  So we need to make one last check before
        // exiting.
        if (Character.toLowerCase(u1) == Character.toLowerCase(u2)) {
          continue;
        }
      }
      return false;
    }
    return true;
  }

  /**
   * Tests if the substring of this string beginning at the
   * specified index starts with the specified prefix.
   *
   * @param prefix the prefix.
   * @param toffset where to begin looking in this string.
   * @return {@code true} if the character sequence represented by the argument is a prefix of the
   * substring of this object starting at index {@code toffset}; {@code false} otherwise. The result
   * is {@code false} if {@code toffset} is negative or greater than the length of this {@code
   * String} object; otherwise the result is the same as the result of the expression
   * <pre>
   *          this.substring(toffset).startsWith(prefix)
   *          </pre>
   */
  public boolean startsWith(String prefix, int toffset) {
    char ta[] = value;
    int to = toffset;
    char pa[] = prefix.value;
    int po = 0;
    int pc = prefix.value.length;
    // Note: toffset might be near -1>>>1.
    if ((toffset < 0) || (toffset > value.length - pc)) {
      return false;
    }
    while (--pc >= 0) {
      if (ta[to++] != pa[po++]) {
        return false;
      }
    }
    return true;
  }

  /**
   * Tests if this string starts with the specified prefix.
   *
   * @param prefix the prefix.
   * @return {@code true} if the character sequence represented by the argument is a prefix of the
   * character sequence represented by this string; {@code false} otherwise. Note also that {@code
   * true} will be returned if the argument is an empty string or is equal to this {@code String}
   * object as determined by the {@link #equals(Object)} method.
   * @since 1. 0
   */
  public boolean startsWith(String prefix) {
    return startsWith(prefix, 0);
  }

  /**
   * Tests if this string ends with the specified suffix.
   *
   * @param suffix the suffix.
   * @return {@code true} if the character sequence represented by the argument is a suffix of the
   * character sequence represented by this object; {@code false} otherwise. Note that the result
   * will be {@code true} if the argument is the empty string or is equal to this {@code String}
   * object as determined by the {@link #equals(Object)} method.
   */
  public boolean endsWith(String suffix) {
    return startsWith(suffix, value.length - suffix.value.length);
  }

  /**
   * Returns a hash code for this string. The hash code for a
   * {@code String} object is computed as
   * <blockquote><pre>
   * s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]
   * </pre></blockquote>
   * using {@code int} arithmetic, where {@code s[i]} is the
   * <i>i</i>th character of the string, {@code n} is the length of
   * the string, and {@code ^} indicates exponentiation.
   * (The hash value of the empty string is zero.)
   *
   * @return a hash code value for this object.
   */
  public int hashCode() {
    int h = hash;
    if (h == 0 && value.length > 0) {
      char val[] = value;

      for (int i = 0; i < value.length; i++) {
        h = 31 * h + val[i];
      }
      hash = h;
    }
    return h;
  }

  /**
   * Returns the index within this string of the first occurrence of
   * the specified character. If a character with value
   * {@code ch} occurs in the character sequence represented by
   * this {@code String} object, then the index (in Unicode
   * code units) of the first such occurrence is returned. For
   * values of {@code ch} in the range from 0 to 0xFFFF
   * (inclusive), this is the smallest value <i>k</i> such that:
   * <blockquote><pre>
   * this.charAt(<i>k</i>) == ch
   * </pre></blockquote>
   * is true. For other values of {@code ch}, it is the
   * smallest value <i>k</i> such that:
   * <blockquote><pre>
   * this.codePointAt(<i>k</i>) == ch
   * </pre></blockquote>
   * is true. In either case, if no such character occurs in this
   * string, then {@code -1} is returned.
   *
   * @param ch a character (Unicode code point).
   * @return the index of the first occurrence of the character in the character sequence
   * represented by this object, or {@code -1} if the character does not occur.
   */
  public int indexOf(int ch) {
    return indexOf(ch, 0);
  }

  /**
   * Returns the index within this string of the first occurrence of the
   * specified character, starting the search at the specified index.
   * <p>
   * If a character with value {@code ch} occurs in the
   * character sequence represented by this {@code String}
   * object at an index no smaller than {@code fromIndex}, then
   * the index of the first such occurrence is returned. For values
   * of {@code ch} in the range from 0 to 0xFFFF (inclusive),
   * this is the smallest value <i>k</i> such that:
   * <blockquote><pre>
   * (this.charAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &gt;= fromIndex)
   * </pre></blockquote>
   * is true. For other values of {@code ch}, it is the
   * smallest value <i>k</i> such that:
   * <blockquote><pre>
   * (this.codePointAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &gt;= fromIndex)
   * </pre></blockquote>
   * is true. In either case, if no such character occurs in this
   * string at or after position {@code fromIndex}, then
   * {@code -1} is returned.
   *
   * <p>
   * There is no restriction on the value of {@code fromIndex}. If it
   * is negative, it has the same effect as if it were zero: this entire
   * string may be searched. If it is greater than the length of this
   * string, it has the same effect as if it were equal to the length of
   * this string: {@code -1} is returned.
   *
   * <p>All indices are specified in {@code char} values
   * (Unicode code units).
   *
   * @param ch a character (Unicode code point).
   * @param fromIndex the index to start the search from.
   * @return the index of the first occurrence of the character in the character sequence
   * represented by this object that is greater than or equal to {@code fromIndex}, or {@code -1} if
   * the character does not occur.
   */
  public int indexOf(int ch, int fromIndex) {
    final int max = value.length;
    if (fromIndex < 0) {
      fromIndex = 0;
    } else if (fromIndex >= max) {
      // Note: fromIndex might be near -1>>>1.
      return -1;
    }

    if (ch < Character.MIN_SUPPLEMENTARY_CODE_POINT) {
      // handle most cases here (ch is a BMP code point or a
      // negative value (invalid code point))
      final char[] value = this.value;
      for (int i = fromIndex; i < max; i++) {
        if (value[i] == ch) {
          return i;
        }
      }
      return -1;
    } else {
      return indexOfSupplementary(ch, fromIndex);
    }
  }

  /**
   * Handles (rare) calls of indexOf with a supplementary character.
   */
  private int indexOfSupplementary(int ch, int fromIndex) {
    if (Character.isValidCodePoint(ch)) {
      final char[] value = this.value;
      final char hi = Character.highSurrogate(ch);
      final char lo = Character.lowSurrogate(ch);
      final int max = value.length - 1;
      for (int i = fromIndex; i < max; i++) {
        if (value[i] == hi && value[i + 1] == lo) {
          return i;
        }
      }
    }
    return -1;
  }

  /**
   * Returns the index within this string of the last occurrence of
   * the specified character. For values of {@code ch} in the
   * range from 0 to 0xFFFF (inclusive), the index (in Unicode code
   * units) returned is the largest value <i>k</i> such that:
   * <blockquote><pre>
   * this.charAt(<i>k</i>) == ch
   * </pre></blockquote>
   * is true. For other values of {@code ch}, it is the
   * largest value <i>k</i> such that:
   * <blockquote><pre>
   * this.codePointAt(<i>k</i>) == ch
   * </pre></blockquote>
   * is true.  In either case, if no such character occurs in this
   * string, then {@code -1} is returned.  The
   * {@code String} is searched backwards starting at the last
   * character.
   *
   * @param ch a character (Unicode code point).
   * @return the index of the last occurrence of the character in the character sequence represented
   * by this object, or {@code -1} if the character does not occur.
   */
  public int lastIndexOf(int ch) {
    return lastIndexOf(ch, value.length - 1);
  }

  /**
   * Returns the index within this string of the last occurrence of
   * the specified character, searching backward starting at the
   * specified index. For values of {@code ch} in the range
   * from 0 to 0xFFFF (inclusive), the index returned is the largest
   * value <i>k</i> such that:
   * <blockquote><pre>
   * (this.charAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &lt;= fromIndex)
   * </pre></blockquote>
   * is true. For other values of {@code ch}, it is the
   * largest value <i>k</i> such that:
   * <blockquote><pre>
   * (this.codePointAt(<i>k</i>) == ch) {@code &&} (<i>k</i> &lt;= fromIndex)
   * </pre></blockquote>
   * is true. In either case, if no such character occurs in this
   * string at or before position {@code fromIndex}, then
   * {@code -1} is returned.
   *
   * <p>All indices are specified in {@code char} values
   * (Unicode code units).
   *
   * @param ch a character (Unicode code point).
   * @param fromIndex the index to start the search from. There is no restriction on the value of
   * {@code fromIndex}. If it is greater than or equal to the length of this string, it has the same
   * effect as if it were equal to one less than the length of this string: this entire string may
   * be searched. If it is negative, it has the same effect as if it were -1: -1 is returned.
   * @return the index of the last occurrence of the character in the character sequence represented
   * by this object that is less than or equal to {@code fromIndex}, or {@code -1} if the character
   * does not occur before that point.
   */
  public int lastIndexOf(int ch, int fromIndex) {
    if (ch < Character.MIN_SUPPLEMENTARY_CODE_POINT) {
      // handle most cases here (ch is a BMP code point or a
      // negative value (invalid code point))
      final char[] value = this.value;
      int i = Math.min(fromIndex, value.length - 1);
      for (; i >= 0; i--) {
        if (value[i] == ch) {
          return i;
        }
      }
      return -1;
    } else {
      return lastIndexOfSupplementary(ch, fromIndex);
    }
  }

  /**
   * Handles (rare) calls of lastIndexOf with a supplementary character.
   */
  private int lastIndexOfSupplementary(int ch, int fromIndex) {
    if (Character.isValidCodePoint(ch)) {
      final char[] value = this.value;
      char hi = Character.highSurrogate(ch);
      char lo = Character.lowSurrogate(ch);
      int i = Math.min(fromIndex, value.length - 2);
      for (; i >= 0; i--) {
        if (value[i] == hi && value[i + 1] == lo) {
          return i;
        }
      }
    }
    return -1;
  }

  /**
   * Returns the index within this string of the first occurrence of the
   * specified substring.
   *
   * <p>The returned index is the smallest value <i>k</i> for which:
   * <blockquote><pre>
   * this.startsWith(str, <i>k</i>)
   * </pre></blockquote>
   * If no such value of <i>k</i> exists, then {@code -1} is returned.
   *
   * @param str the substring to search for.
   * @return the index of the first occurrence of the specified substring, or {@code -1} if there is
   * no such occurrence.
   */
  public int indexOf(String str) {
    return indexOf(str, 0);
  }

  /**
   * Returns the index within this string of the first occurrence of the
   * specified substring, starting at the specified index.
   *
   * <p>The returned index is the smallest value <i>k</i> for which:
   * <blockquote><pre>
   * <i>k</i> &gt;= fromIndex {@code &&} this.startsWith(str, <i>k</i>)
   * </pre></blockquote>
   * If no such value of <i>k</i> exists, then {@code -1} is returned.
   *
   * @param str the substring to search for.
   * @param fromIndex the index from which to start the search.
   * @return the index of the first occurrence of the specified substring, starting at the specified
   * index, or {@code -1} if there is no such occurrence.
   */
  public int indexOf(String str, int fromIndex) {
    return indexOf(value, 0, value.length,
        str.value, 0, str.value.length, fromIndex);
  }

  /**
   * Code shared by String and AbstractStringBuilder to do searches. The
   * source is the character array being searched, and the target
   * is the string being searched for.
   *
   * @param source the characters being searched.
   * @param sourceOffset offset of the source string.
   * @param sourceCount count of the source string.
   * @param target the characters being searched for.
   * @param fromIndex the index to begin searching from.
   */
  static int indexOf(char[] source, int sourceOffset, int sourceCount,
      String target, int fromIndex) {
    return indexOf(source, sourceOffset, sourceCount,
        target.value, 0, target.value.length,
        fromIndex);
  }

  /**
   * Code shared by String and StringBuffer to do searches. The
   * source is the character array being searched, and the target
   * is the string being searched for.
   *
   * @param source the characters being searched.
   * @param sourceOffset offset of the source string.
   * @param sourceCount count of the source string.
   * @param target the characters being searched for.
   * @param targetOffset offset of the target string.
   * @param targetCount count of the target string.
   * @param fromIndex the index to begin searching from.
   */
  static int indexOf(char[] source, int sourceOffset, int sourceCount,
      char[] target, int targetOffset, int targetCount,
      int fromIndex) {
    if (fromIndex >= sourceCount) {
      return (targetCount == 0 ? sourceCount : -1);
    }
    if (fromIndex < 0) {
      fromIndex = 0;
    }
    if (targetCount == 0) {
      return fromIndex;
    }

    char first = target[targetOffset];
    int max = sourceOffset + (sourceCount - targetCount);

    for (int i = sourceOffset + fromIndex; i <= max; i++) {
            /* Look for first character. */
      if (source[i] != first) {
        while (++i <= max && source[i] != first) {
          ;
        }
      }

            /* Found first character, now look at the rest of v2 */
      if (i <= max) {
        int j = i + 1;
        int end = j + targetCount - 1;
        for (int k = targetOffset + 1; j < end && source[j]
            == target[k]; j++, k++) {
          ;
        }

        if (j == end) {
                    /* Found whole string. */
          return i - sourceOffset;
        }
      }
    }
    return -1;
  }

  /**
   * Returns the index within this string of the last occurrence of the
   * specified substring.  The last occurrence of the empty string ""
   * is considered to occur at the index value {@code this.length()}.
   *
   * <p>The returned index is the largest value <i>k</i> for which:
   * <blockquote><pre>
   * this.startsWith(str, <i>k</i>)
   * </pre></blockquote>
   * If no such value of <i>k</i> exists, then {@code -1} is returned.
   *
   * @param str the substring to search for.
   * @return the index of the last occurrence of the specified substring, or {@code -1} if there is
   * no such occurrence.
   */
  public int lastIndexOf(String str) {
    return lastIndexOf(str, value.length);
  }

  /**
   * Returns the index within this string of the last occurrence of the
   * specified substring, searching backward starting at the specified index.
   *
   * <p>The returned index is the largest value <i>k</i> for which:
   * <blockquote><pre>
   * <i>k</i> {@code <=} fromIndex {@code &&} this.startsWith(str, <i>k</i>)
   * </pre></blockquote>
   * If no such value of <i>k</i> exists, then {@code -1} is returned.
   *
   * @param str the substring to search for.
   * @param fromIndex the index to start the search from.
   * @return the index of the last occurrence of the specified substring, searching backward from
   * the specified index, or {@code -1} if there is no such occurrence.
   */
  public int lastIndexOf(String str, int fromIndex) {
    return lastIndexOf(value, 0, value.length,
        str.value, 0, str.value.length, fromIndex);
  }

  /**
   * Code shared by String and AbstractStringBuilder to do searches. The
   * source is the character array being searched, and the target
   * is the string being searched for.
   *
   * @param source the characters being searched.
   * @param sourceOffset offset of the source string.
   * @param sourceCount count of the source string.
   * @param target the characters being searched for.
   * @param fromIndex the index to begin searching from.
   */
  static int lastIndexOf(char[] source, int sourceOffset, int sourceCount,
      String target, int fromIndex) {
    return lastIndexOf(source, sourceOffset, sourceCount,
        target.value, 0, target.value.length,
        fromIndex);
  }

  /**
   * Code shared by String and StringBuffer to do searches. The
   * source is the character array being searched, and the target
   * is the string being searched for.
   *
   * @param source the characters being searched.
   * @param sourceOffset offset of the source string.
   * @param sourceCount count of the source string.
   * @param target the characters being searched for.
   * @param targetOffset offset of the target string.
   * @param targetCount count of the target string.
   * @param fromIndex the index to begin searching from.
   */
  static int lastIndexOf(char[] source, int sourceOffset, int sourceCount,
      char[] target, int targetOffset, int targetCount,
      int fromIndex) {
        /*
         * Check arguments; return immediately where possible. For
         * consistency, don't check for null str.
         */
    int rightIndex = sourceCount - targetCount;
    if (fromIndex < 0) {
      return -1;
    }
    if (fromIndex > rightIndex) {
      fromIndex = rightIndex;
    }
        /* Empty string always matches. */
    if (targetCount == 0) {
      return fromIndex;
    }

    int strLastIndex = targetOffset + targetCount - 1;
    char strLastChar = target[strLastIndex];
    int min = sourceOffset + targetCount - 1;
    int i = min + fromIndex;

    startSearchForLastChar:
    while (true) {
      while (i >= min && source[i] != strLastChar) {
        i--;
      }
      if (i < min) {
        return -1;
      }
      int j = i - 1;
      int start = j - (targetCount - 1);
      int k = strLastIndex - 1;

      while (j > start) {
        if (source[j--] != target[k--]) {
          i--;
          continue startSearchForLastChar;
        }
      }
      return start - sourceOffset + 1;
    }
  }

  /**
   * Returns a string that is a substring of this string. The
   * substring begins with the character at the specified index and
   * extends to the end of this string. <p>
   * Examples:
   * <blockquote><pre>
   * "unhappy".substring(2) returns "happy"
   * "Harbison".substring(3) returns "bison"
   * "emptiness".substring(9) returns "" (an empty string)
   * </pre></blockquote>
   *
   * @param beginIndex the beginning index, inclusive.
   * @return the specified substring.
   * @throws IndexOutOfBoundsException if {@code beginIndex} is negative or larger than the length
   * of this {@code String} object.
   */
  public String substring(int beginIndex) {
    if (beginIndex < 0) {
      throw new StringIndexOutOfBoundsException(beginIndex);
    }
    int subLen = value.length - beginIndex;
    if (subLen < 0) {
      throw new StringIndexOutOfBoundsException(subLen);
    }
    return (beginIndex == 0) ? this : new String(value, beginIndex, subLen);
  }

  /**
   * Returns a string that is a substring of this string. The
   * substring begins at the specified {@code beginIndex} and
   * extends to the character at index {@code endIndex - 1}.
   * Thus the length of the substring is {@code endIndex-beginIndex}.
   * <p>
   * Examples:
   * <blockquote><pre>
   * "hamburger".substring(4, 8) returns "urge"
   * "smiles".substring(1, 5) returns "mile"
   * </pre></blockquote>
   *
   * @param beginIndex the beginning index, inclusive.
   * @param endIndex the ending index, exclusive.
   * @return the specified substring.
   * @throws IndexOutOfBoundsException if the {@code beginIndex} is negative, or {@code endIndex} is
   * larger than the length of this {@code String} object, or {@code beginIndex} is larger than
   * {@code endIndex}.
   */
  public String substring(int beginIndex, int endIndex) {
    if (beginIndex < 0) {
      throw new StringIndexOutOfBoundsException(beginIndex);
    }
    if (endIndex > value.length) {
      throw new StringIndexOutOfBoundsException(endIndex);
    }
    int subLen = endIndex - beginIndex;
    if (subLen < 0) {
      throw new StringIndexOutOfBoundsException(subLen);
    }
    return ((beginIndex == 0) && (endIndex == value.length)) ? this
        : new String(value, beginIndex, subLen);
  }

  /**
   * Returns a character sequence that is a subsequence of this sequence.
   *
   * <p> An invocation of this method of the form
   *
   * <blockquote><pre>
   * str.subSequence(begin,&nbsp;end)</pre></blockquote>
   *
   * behaves in exactly the same way as the invocation
   *
   * <blockquote><pre>
   * str.substring(begin,&nbsp;end)</pre></blockquote>
   *
   * @param beginIndex the begin index, inclusive.
   * @param endIndex the end index, exclusive.
   * @return the specified subsequence.
   * @throws IndexOutOfBoundsException if {@code beginIndex} or {@code endIndex} is negative, if
   * {@code endIndex} is greater than {@code length()}, or if {@code beginIndex} is greater than
   * {@code endIndex}
   * @apiNote This method is defined so that the {@code String} class can implement the {@link
   * CharSequence} interface.
   * @spec JSR-51
   * @since 1.4
   */
  public CharSequence subSequence(int beginIndex, int endIndex) {
    return this.substring(beginIndex, endIndex);
  }

  /**
   * Concatenates the specified string to the end of this string.
   * <p>
   * If the length of the argument string is {@code 0}, then this
   * {@code String} object is returned. Otherwise, a
   * {@code String} object is returned that represents a character
   * sequence that is the concatenation of the character sequence
   * represented by this {@code String} object and the character
   * sequence represented by the argument string.<p>
   * Examples:
   * <blockquote><pre>
   * "cares".concat("s") returns "caress"
   * "to".concat("get").concat("her") returns "together"
   * </pre></blockquote>
   *
   * @param str the {@code String} that is concatenated to the end of this {@code String}.
   * @return a string that represents the concatenation of this object's characters followed by the
   * string argument's characters.
   */
  public String concat(String str) {
    int otherLen = str.length();
    if (otherLen == 0) {
      return this;
    }
    int len = value.length;
    char buf[] = Arrays.copyOf(value, len + otherLen);
    str.getChars(buf, len);
    return new String(buf, true);
  }

  /**
   * Returns a string resulting from replacing all occurrences of
   * {@code oldChar} in this string with {@code newChar}.
   * <p>
   * If the character {@code oldChar} does not occur in the
   * character sequence represented by this {@code String} object,
   * then a reference to this {@code String} object is returned.
   * Otherwise, a {@code String} object is returned that
   * represents a character sequence identical to the character sequence
   * represented by this {@code String} object, except that every
   * occurrence of {@code oldChar} is replaced by an occurrence
   * of {@code newChar}.
   * <p>
   * Examples:
   * <blockquote><pre>
   * "mesquite in your cellar".replace('e', 'o')
   *         returns "mosquito in your collar"
   * "the war of baronets".replace('r', 'y')
   *         returns "the way of bayonets"
   * "sparring with a purple porpoise".replace('p', 't')
   *         returns "starring with a turtle tortoise"
   * "JonL".replace('q', 'x') returns "JonL" (no change)
   * </pre></blockquote>
   *
   * @param oldChar the old character.
   * @param newChar the new character.
   * @return a string derived from this string by replacing every occurrence of {@code oldChar} with
   * {@code newChar}.
   */
  public String replace(char oldChar, char newChar) {
    if (oldChar != newChar) {
      int len = value.length;
      int i = -1;
      char[] val = value; /* avoid getfield opcode */

      while (++i < len) {
        if (val[i] == oldChar) {
          break;
        }
      }
      if (i < len) {
        char buf[] = new char[len];
        for (int j = 0; j < i; j++) {
          buf[j] = val[j];
        }
        while (i < len) {
          char c = val[i];
          buf[i] = (c == oldChar) ? newChar : c;
          i++;
        }
        return new String(buf, true);
      }
    }
    return this;
  }

  /**
   * Tells whether or not this string matches the given <a
   * href="../util/regex/Pattern.html#sum">regular expression</a>.
   *
   * <p> An invocation of this method of the form
   * <i>str</i>{@code .matches(}<i>regex</i>{@code )} yields exactly the
   * same result as the expression
   *
   * <blockquote>
   * {@link java.util.regex.Pattern}.{@link java.util.regex.Pattern#matches(String, CharSequence)
   * matches(<i>regex</i>, <i>str</i>)}
   * </blockquote>
   *
   * @param regex the regular expression to which this string is to be matched
   * @return {@code true} if, and only if, this string matches the given regular expression
   * @throws PatternSyntaxException if the regular expression's syntax is invalid
   * @spec JSR-51
   * @see java.util.regex.Pattern
   * @since 1.4
   */
  public boolean matches(String regex) {
    return Pattern.matches(regex, this);
  }

  /**
   * Returns true if and only if this string contains the specified
   * sequence of char values.
   *
   * @param s the sequence to search for
   * @return true if this string contains {@code s}, false otherwise
   * @since 1.5
   */
  public boolean contains(CharSequence s) {
    return indexOf(s.toString()) > -1;
  }

  /**
   * Replaces the first substring of this string that matches the given <a
   * href="../util/regex/Pattern.html#sum">regular expression</a> with the
   * given replacement.
   *
   * <p> An invocation of this method of the form
   * <i>str</i>{@code .replaceFirst(}<i>regex</i>{@code ,} <i>repl</i>{@code )}
   * yields exactly the same result as the expression
   *
   * <blockquote>
   * <code>
   * {@link java.util.regex.Pattern}.{@link
   * java.util.regex.Pattern#compile compile}(<i>regex</i>).{@link
   * java.util.regex.Pattern#matcher(java.lang.CharSequence) matcher}(<i>str</i>).{@link
   * java.util.regex.Matcher#replaceFirst replaceFirst}(<i>repl</i>)
   * </code>
   * </blockquote>
   *
   * <p>
   * Note that backslashes ({@code \}) and dollar signs ({@code $}) in the
   * replacement string may cause the results to be different than if it were
   * being treated as a literal replacement string; see
   * {@link java.util.regex.Matcher#replaceFirst}.
   * Use {@link java.util.regex.Matcher#quoteReplacement} to suppress the special
   * meaning of these characters, if desired.
   *
   * @param regex the regular expression to which this string is to be matched
   * @param replacement the string to be substituted for the first match
   * @return The resulting {@code String}
   * @throws PatternSyntaxException if the regular expression's syntax is invalid
   * @spec JSR-51
   * @see java.util.regex.Pattern
   * @since 1.4
   */
  public String replaceFirst(String regex, String replacement) {
    return Pattern.compile(regex).matcher(this).replaceFirst(replacement);
  }

  /**
   * Replaces each substring of this string that matches the given <a
   * href="../util/regex/Pattern.html#sum">regular expression</a> with the
   * given replacement.
   *
   * <p> An invocation of this method of the form
   * <i>str</i>{@code .replaceAll(}<i>regex</i>{@code ,} <i>repl</i>{@code )}
   * yields exactly the same result as the expression
   *
   * <blockquote>
   * <code>
   * {@link java.util.regex.Pattern}.{@link
   * java.util.regex.Pattern#compile compile}(<i>regex</i>).{@link
   * java.util.regex.Pattern#matcher(java.lang.CharSequence) matcher}(<i>str</i>).{@link
   * java.util.regex.Matcher#replaceAll replaceAll}(<i>repl</i>)
   * </code>
   * </blockquote>
   *
   * <p>
   * Note that backslashes ({@code \}) and dollar signs ({@code $}) in the
   * replacement string may cause the results to be different than if it were
   * being treated as a literal replacement string; see
   * {@link java.util.regex.Matcher#replaceAll Matcher.replaceAll}.
   * Use {@link java.util.regex.Matcher#quoteReplacement} to suppress the special
   * meaning of these characters, if desired.
   *
   * @param regex the regular expression to which this string is to be matched
   * @param replacement the string to be substituted for each match
   * @return The resulting {@code String}
   * @throws PatternSyntaxException if the regular expression's syntax is invalid
   * @spec JSR-51
   * @see java.util.regex.Pattern
   * @since 1.4
   */
  public String replaceAll(String regex, String replacement) {
    return Pattern.compile(regex).matcher(this).replaceAll(replacement);
  }

  /**
   * Replaces each substring of this string that matches the literal target
   * sequence with the specified literal replacement sequence. The
   * replacement proceeds from the beginning of the string to the end, for
   * example, replacing "aa" with "b" in the string "aaa" will result in
   * "ba" rather than "ab".
   *
   * @param target The sequence of char values to be replaced
   * @param replacement The replacement sequence of char values
   * @return The resulting string
   * @since 1.5
   */
  public String replace(CharSequence target, CharSequence replacement) {
    return Pattern.compile(target.toString(), Pattern.LITERAL).matcher(
        this).replaceAll(Matcher.quoteReplacement(replacement.toString()));
  }

  /**
   * Splits this string around matches of the given <a href="../util/regex/Pattern.html#sum">regular
   * expression</a>.
   *
   * <p> The array returned by this method contains each substring of this string that is terminated
   * by another substring that matches the given expression or is terminated by the end of the
   * string.  The substrings in the array are in the order in which they occur in this string.  If
   * the expression does not match any part of the input then the resulting array has just one
   * element, namely this string.
   *
   * <p> When there is a positive-width match at the beginning of this string then an empty leading
   * substring is included at the beginning of the resulting array. A zero-width match at the
   * beginning however never produces such empty leading substring.
   *
   * <p> The {@code limit} parameter controls the number of times the pattern is applied and
   * therefore affects the length of the resulting array.  If the limit <i>n</i> is greater than
   * zero then the pattern will be applied at most <i>n</i>&nbsp;-&nbsp;1 times, the array's length
   * will be no greater than <i>n</i>, and the array's last entry will contain all input beyond the
   * last matched delimiter.  If <i>n</i> is non-positive then the pattern will be applied as many
   * times as possible and the array can have any length.  If <i>n</i> is zero then the pattern will
   * be applied as many times as possible, the array can have any length, and trailing empty strings
   * will be discarded.
   *
   * <p> The string {@code "boo:and:foo"}, for example, yields the following results with these
   * parameters:
   *
   * <blockquote><table cellpadding=1 cellspacing=0 summary="Split example showing regex, limit, and
   * result"> <tr> <th>Regex</th> <th>Limit</th> <th>Result</th> </tr> <tr><td align=center>:</td>
   * <td align=center>2</td> <td>{@code { "boo", "and:foo" }}</td></tr> <tr><td align=center>:</td>
   * <td align=center>5</td> <td>{@code { "boo", "and", "foo" }}</td></tr> <tr><td
   * align=center>:</td> <td align=center>-2</td> <td>{@code { "boo", "and", "foo" }}</td></tr>
   * <tr><td align=center>o</td> <td align=center>5</td> <td>{@code { "b", "", ":and:f", "", ""
   * }}</td></tr> <tr><td align=center>o</td> <td align=center>-2</td> <td>{@code { "b", "",
   * ":and:f", "", "" }}</td></tr> <tr><td align=center>o</td> <td align=center>0</td> <td>{@code {
   * "b", "", ":and:f" }}</td></tr> </table></blockquote>
   *
   * <p> An invocation of this method of the form <i>str.</i>{@code split(}<i>regex</i>{@code
   * ,}&nbsp;<i>n</i>{@code )} yields the same result as the expression
   *
   * <blockquote> <code> {@link java.util.regex.Pattern}.{@link java.util.regex.Pattern#compile
   * compile}(<i>regex</i>).{@link java.util.regex.Pattern#split(java.lang.CharSequence, int)
   * split}(<i>str</i>,&nbsp;<i>n</i>) </code> </blockquote>
   *
   * @param regex the delimiting regular expression
   * @param limit the result threshold, as described above
   * @return the array of strings computed by splitting this string around matches of the given
   * regular expression
   * @throws PatternSyntaxException if the regular expression's syntax is invalid
   * @spec JSR-51
   * @see java.util.regex.Pattern
   * @since 1.4
   */
  public String[] split(String regex, int limit) {
        /* fastpath if the regex is a
         (1)one-char String and this character is not one of the
            RegEx's meta characters ".$|()[{^?*+\\", or
         (2)two-char String and the first char is the backslash and
            the second is not the ascii digit or ascii letter.
         */
    char ch = 0;
    if (((regex.value.length == 1 &&
        ".$|()[{^?*+\\".indexOf(ch = regex.charAt(0)) == -1) ||
        (regex.length() == 2 &&
            regex.charAt(0) == '\\' &&
            (((ch = regex.charAt(1)) - '0') | ('9' - ch)) < 0 &&
            ((ch - 'a') | ('z' - ch)) < 0 &&
            ((ch - 'A') | ('Z' - ch)) < 0)) &&
        (ch < Character.MIN_HIGH_SURROGATE ||
            ch > Character.MAX_LOW_SURROGATE)) {
      int off = 0;
      int next = 0;
      boolean limited = limit > 0;
      ArrayList<String> list = new ArrayList<>();
      while ((next = indexOf(ch, off)) != -1) {
        if (!limited || list.size() < limit - 1) {
          list.add(substring(off, next));
          off = next + 1;
        } else {    // last one
          //assert (list.size() == limit - 1);
          list.add(substring(off, value.length));
          off = value.length;
          break;
        }
      }
      // If no match was found, return this
      if (off == 0) {
        return new String[]{this};
      }

      // Add remaining segment
      if (!limited || list.size() < limit) {
        list.add(substring(off, value.length));
      }

      // Construct result
      int resultSize = list.size();
      if (limit == 0) {
        while (resultSize > 0 && list.get(resultSize - 1).length() == 0) {
          resultSize--;
        }
      }
      String[] result = new String[resultSize];
      return list.subList(0, resultSize).toArray(result);
    }
    return Pattern.compile(regex).split(this, limit);
  }

  /**
   * Splits this string around matches of the given <a href="../util/regex/Pattern.html#sum">regular
   * expression</a>.
   *
   * <p> This method works as if by invoking the two-argument {@link #split(String, int) split}
   * method with the given expression and a limit argument of zero.  Trailing empty strings are
   * therefore not included in the resulting array.
   *
   * <p> The string {@code "boo:and:foo"}, for example, yields the following results with these
   * expressions:
   *
   * <blockquote><table cellpadding=1 cellspacing=0 summary="Split examples showing regex and
   * result"> <tr> <th>Regex</th> <th>Result</th> </tr> <tr><td align=center>:</td> <td>{@code {
   * "boo", "and", "foo" }}</td></tr> <tr><td align=center>o</td> <td>{@code { "b", "", ":and:f"
   * }}</td></tr> </table></blockquote>
   *
   * @param regex the delimiting regular expression
   * @return the array of strings computed by splitting this string around matches of the given
   * regular expression
   * @throws PatternSyntaxException if the regular expression's syntax is invalid
   * @spec JSR-51
   * @see java.util.regex.Pattern
   * @since 1.4
   */
  public String[] split(String regex) {
    return split(regex, 0);
  }

  /**
   * Returns a new String composed of copies of the
   * {@code CharSequence elements} joined together with a copy of
   * the specified {@code delimiter}.
   *
   * <blockquote>For example,
   * <pre>{@code
   *     String message = String.join("-", "Java", "is", "cool");
   *     // message returned is: "Java-is-cool"
   * }</pre></blockquote>
   *
   * Note that if an element is null, then {@code "null"} is added.
   *
   * @param delimiter the delimiter that separates each element
   * @param elements the elements to join together.
   * @return a new {@code String} that is composed of the {@code elements} separated by the {@code
   * delimiter}
   * @throws NullPointerException If {@code delimiter} or {@code elements} is {@code null}
   * @see java.util.StringJoiner
   * @since 1.8
   */
  public static String join(CharSequence delimiter, CharSequence... elements) {
    Objects.requireNonNull(delimiter);
    Objects.requireNonNull(elements);
    // Number of elements not likely worth Arrays.stream overhead.
    StringJoiner joiner = new StringJoiner(delimiter);
    for (CharSequence cs : elements) {
      joiner.add(cs);
    }
    return joiner.toString();
  }

  /**
   * Returns a new {@code String} composed of copies of the
   * {@code CharSequence elements} joined together with a copy of the
   * specified {@code delimiter}.
   *
   * <blockquote>For example,
   * <pre>{@code
   *     List<String> strings = new LinkedList<>();
   *     strings.add("Java");strings.add("is");
   *     strings.add("cool");
   *     String message = String.join(" ", strings);
   *     //message returned is: "Java is cool"
   *
   *     Set<String> strings = new LinkedHashSet<>();
   *     strings.add("Java"); strings.add("is");
   *     strings.add("very"); strings.add("cool");
   *     String message = String.join("-", strings);
   *     //message returned is: "Java-is-very-cool"
   * }</pre></blockquote>
   *
   * Note that if an individual element is {@code null}, then {@code "null"} is added.
   *
   * @param delimiter a sequence of characters that is used to separate each of the {@code elements}
   * in the resulting {@code String}
   * @param elements an {@code Iterable} that will have its {@code elements} joined together.
   * @return a new {@code String} that is composed from the {@code elements} argument
   * @throws NullPointerException If {@code delimiter} or {@code elements} is {@code null}
   * @see #join(CharSequence, CharSequence...)
   * @see java.util.StringJoiner
   * @since 1.8
   */
  public static String join(CharSequence delimiter,
      Iterable<? extends CharSequence> elements) {
    Objects.requireNonNull(delimiter);
    Objects.requireNonNull(elements);
    StringJoiner joiner = new StringJoiner(delimiter);
    for (CharSequence cs : elements) {
      joiner.add(cs);
    }
    return joiner.toString();
  }

  /**
   * Converts all of the characters in this {@code String} to lower case using the rules of the
   * given {@code Locale}.  Case mapping is based on the Unicode Standard version specified by the
   * {@link java.lang.Character Character} class. Since case mappings are not always 1:1 char
   * mappings, the resulting {@code String} may be a different length than the original {@code
   * String}. <p> Examples of lowercase  mappings are in the following table: <table border="1"
   * summary="Lowercase mapping examples showing language code of locale, upper case, lower case,
   * and description"> <tr> <th>Language Code of Locale</th> <th>Upper Case</th> <th>Lower Case</th>
   * <th>Description</th> </tr> <tr> <td>tr (Turkish)</td> <td>&#92;u0130</td> <td>&#92;u0069</td>
   * <td>capital letter I with dot above -&gt; small letter i</td> </tr> <tr> <td>tr (Turkish)</td>
   * <td>&#92;u0049</td> <td>&#92;u0131</td> <td>capital letter I -&gt; small letter dotless i </td>
   * </tr> <tr> <td>(all)</td> <td>French Fries</td> <td>french fries</td> <td>lowercased all chars
   * in String</td> </tr> <tr> <td>(all)</td> <td><img src="doc-files/capiota.gif"
   * alt="capiota"><img src="doc-files/capchi.gif" alt="capchi"> <img src="doc-files/captheta.gif"
   * alt="captheta"><img src="doc-files/capupsil.gif" alt="capupsil"> <img
   * src="doc-files/capsigma.gif" alt="capsigma"></td> <td><img src="doc-files/iota.gif"
   * alt="iota"><img src="doc-files/chi.gif" alt="chi"> <img src="doc-files/theta.gif"
   * alt="theta"><img src="doc-files/upsilon.gif" alt="upsilon"> <img src="doc-files/sigma1.gif"
   * alt="sigma"></td> <td>lowercased all chars in String</td> </tr> </table>
   *
   * @param locale use the case transformation rules for this locale
   * @return the {@code String}, converted to lowercase.
   * @see java.lang.String#toLowerCase()
   * @see java.lang.String#toUpperCase()
   * @see java.lang.String#toUpperCase(Locale)
   * @since 1.1
   */
  public String toLowerCase(Locale locale) {
    if (locale == null) {
      throw new NullPointerException();
    }

    int firstUpper;
    final int len = value.length;

        /* Now check if there are any characters that need to be changed. */
    scan:
    {
      for (firstUpper = 0; firstUpper < len; ) {
        char c = value[firstUpper];
        if ((c >= Character.MIN_HIGH_SURROGATE)
            && (c <= Character.MAX_HIGH_SURROGATE)) {
          int supplChar = codePointAt(firstUpper);
          if (supplChar != Character.toLowerCase(supplChar)) {
            break scan;
          }
          firstUpper += Character.charCount(supplChar);
        } else {
          if (c != Character.toLowerCase(c)) {
            break scan;
          }
          firstUpper++;
        }
      }
      return this;
    }

    char[] result = new char[len];
    int resultOffset = 0;  /* result may grow, so i+resultOffset
                                * is the write location in result */

        /* Just copy the first few lowerCase characters. */
    System.arraycopy(value, 0, result, 0, firstUpper);

    String lang = locale.getLanguage();
    boolean localeDependent =
        (lang == "tr" || lang == "az" || lang == "lt");
    char[] lowerCharArray;
    int lowerChar;
    int srcChar;
    int srcCount;
    for (int i = firstUpper; i < len; i += srcCount) {
      srcChar = (int) value[i];
      if ((char) srcChar >= Character.MIN_HIGH_SURROGATE
          && (char) srcChar <= Character.MAX_HIGH_SURROGATE) {
        srcChar = codePointAt(i);
        srcCount = Character.charCount(srcChar);
      } else {
        srcCount = 1;
      }
      if (localeDependent ||
          srcChar == '\u03A3' || // GREEK CAPITAL LETTER SIGMA
          srcChar == '\u0130') { // LATIN CAPITAL LETTER I WITH DOT ABOVE
        lowerChar = ConditionalSpecialCasing.toLowerCaseEx(this, i, locale);
      } else {
        lowerChar = Character.toLowerCase(srcChar);
      }
      if ((lowerChar == Character.ERROR)
          || (lowerChar >= Character.MIN_SUPPLEMENTARY_CODE_POINT)) {
        if (lowerChar == Character.ERROR) {
          lowerCharArray =
              ConditionalSpecialCasing.toLowerCaseCharArray(this, i, locale);
        } else if (srcCount == 2) {
          resultOffset += Character.toChars(lowerChar, result, i + resultOffset) - srcCount;
          continue;
        } else {
          lowerCharArray = Character.toChars(lowerChar);
        }

                /* Grow result if needed */
        int mapLen = lowerCharArray.length;
        if (mapLen > srcCount) {
          char[] result2 = new char[result.length + mapLen - srcCount];
          System.arraycopy(result, 0, result2, 0, i + resultOffset);
          result = result2;
        }
        for (int x = 0; x < mapLen; ++x) {
          result[i + resultOffset + x] = lowerCharArray[x];
        }
        resultOffset += (mapLen - srcCount);
      } else {
        result[i + resultOffset] = (char) lowerChar;
      }
    }
    return new String(result, 0, len + resultOffset);
  }

  /**
   * Converts all of the characters in this {@code String} to lower
   * case using the rules of the default locale. This is equivalent to calling
   * {@code toLowerCase(Locale.getDefault())}.
   * <p>
   * <b>Note:</b> This method is locale sensitive, and may produce unexpected
   * results if used for strings that are intended to be interpreted locale
   * independently.
   * Examples are programming language identifiers, protocol keys, and HTML
   * tags.
   * For instance, {@code "TITLE".toLowerCase()} in a Turkish locale
   * returns {@code "t\u005Cu0131tle"}, where '\u005Cu0131' is the
   * LATIN SMALL LETTER DOTLESS I character.
   * To obtain correct results for locale insensitive strings, use
   * {@code toLowerCase(Locale.ROOT)}.
   * <p>
   *
   * @return the {@code String}, converted to lowercase.
   * @see java.lang.String#toLowerCase(Locale)
   */
  public String toLowerCase() {
    return toLowerCase(Locale.getDefault());
  }

  /**
   * Converts all of the characters in this {@code String} to upper case using the rules of the
   * given {@code Locale}. Case mapping is based on the Unicode Standard version specified by the
   * {@link java.lang.Character Character} class. Since case mappings are not always 1:1 char
   * mappings, the resulting {@code String} may be a different length than the original {@code
   * String}. <p> Examples of locale-sensitive and 1:M case mappings are in the following table.
   *
   * <table border="1" summary="Examples of locale-sensitive and 1:M case mappings. Shows Language
   * code of locale, lower case, upper case, and description."> <tr> <th>Language Code of
   * Locale</th> <th>Lower Case</th> <th>Upper Case</th> <th>Description</th> </tr> <tr> <td>tr
   * (Turkish)</td> <td>&#92;u0069</td> <td>&#92;u0130</td> <td>small letter i -&gt; capital letter
   * I with dot above</td> </tr> <tr> <td>tr (Turkish)</td> <td>&#92;u0131</td> <td>&#92;u0049</td>
   * <td>small letter dotless i -&gt; capital letter I</td> </tr> <tr> <td>(all)</td>
   * <td>&#92;u00df</td> <td>&#92;u0053 &#92;u0053</td> <td>small letter sharp s -&gt; two letters:
   * SS</td> </tr> <tr> <td>(all)</td> <td>Fahrvergn&uuml;gen</td> <td>FAHRVERGN&Uuml;GEN</td>
   * <td></td> </tr> </table>
   *
   * @param locale use the case transformation rules for this locale
   * @return the {@code String}, converted to uppercase.
   * @see java.lang.String#toUpperCase()
   * @see java.lang.String#toLowerCase()
   * @see java.lang.String#toLowerCase(Locale)
   * @since 1.1
   */
  public String toUpperCase(Locale locale) {
    if (locale == null) {
      throw new NullPointerException();
    }

    int firstLower;
    final int len = value.length;

        /* Now check if there are any characters that need to be changed. */
    scan:
    {
      for (firstLower = 0; firstLower < len; ) {
        int c = (int) value[firstLower];
        int srcCount;
        if ((c >= Character.MIN_HIGH_SURROGATE)
            && (c <= Character.MAX_HIGH_SURROGATE)) {
          c = codePointAt(firstLower);
          srcCount = Character.charCount(c);
        } else {
          srcCount = 1;
        }
        int upperCaseChar = Character.toUpperCaseEx(c);
        if ((upperCaseChar == Character.ERROR)
            || (c != upperCaseChar)) {
          break scan;
        }
        firstLower += srcCount;
      }
      return this;
    }

        /* result may grow, so i+resultOffset is the write location in result */
    int resultOffset = 0;
    char[] result = new char[len]; /* may grow */

        /* Just copy the first few upperCase characters. */
    System.arraycopy(value, 0, result, 0, firstLower);

    String lang = locale.getLanguage();
    boolean localeDependent =
        (lang == "tr" || lang == "az" || lang == "lt");
    char[] upperCharArray;
    int upperChar;
    int srcChar;
    int srcCount;
    for (int i = firstLower; i < len; i += srcCount) {
      srcChar = (int) value[i];
      if ((char) srcChar >= Character.MIN_HIGH_SURROGATE &&
          (char) srcChar <= Character.MAX_HIGH_SURROGATE) {
        srcChar = codePointAt(i);
        srcCount = Character.charCount(srcChar);
      } else {
        srcCount = 1;
      }
      if (localeDependent) {
        upperChar = ConditionalSpecialCasing.toUpperCaseEx(this, i, locale);
      } else {
        upperChar = Character.toUpperCaseEx(srcChar);
      }
      if ((upperChar == Character.ERROR)
          || (upperChar >= Character.MIN_SUPPLEMENTARY_CODE_POINT)) {
        if (upperChar == Character.ERROR) {
          if (localeDependent) {
            upperCharArray =
                ConditionalSpecialCasing.toUpperCaseCharArray(this, i, locale);
          } else {
            upperCharArray = Character.toUpperCaseCharArray(srcChar);
          }
        } else if (srcCount == 2) {
          resultOffset += Character.toChars(upperChar, result, i + resultOffset) - srcCount;
          continue;
        } else {
          upperCharArray = Character.toChars(upperChar);
        }

                /* Grow result if needed */
        int mapLen = upperCharArray.length;
        if (mapLen > srcCount) {
          char[] result2 = new char[result.length + mapLen - srcCount];
          System.arraycopy(result, 0, result2, 0, i + resultOffset);
          result = result2;
        }
        for (int x = 0; x < mapLen; ++x) {
          result[i + resultOffset + x] = upperCharArray[x];
        }
        resultOffset += (mapLen - srcCount);
      } else {
        result[i + resultOffset] = (char) upperChar;
      }
    }
    return new String(result, 0, len + resultOffset);
  }

  /**
   * Converts all of the characters in this {@code String} to upper
   * case using the rules of the default locale. This method is equivalent to
   * {@code toUpperCase(Locale.getDefault())}.
   * <p>
   * <b>Note:</b> This method is locale sensitive, and may produce unexpected
   * results if used for strings that are intended to be interpreted locale
   * independently.
   * Examples are programming language identifiers, protocol keys, and HTML
   * tags.
   * For instance, {@code "title".toUpperCase()} in a Turkish locale
   * returns {@code "T\u005Cu0130TLE"}, where '\u005Cu0130' is the
   * LATIN CAPITAL LETTER I WITH DOT ABOVE character.
   * To obtain correct results for locale insensitive strings, use
   * {@code toUpperCase(Locale.ROOT)}.
   * <p>
   *
   * @return the {@code String}, converted to uppercase.
   * @see java.lang.String#toUpperCase(Locale)
   */
  public String toUpperCase() {
    return toUpperCase(Locale.getDefault());
  }

  /**
   * Returns a string whose value is this string, with any leading and trailing
   * whitespace removed.
   * <p>
   * If this {@code String} object represents an empty character
   * sequence, or the first and last characters of character sequence
   * represented by this {@code String} object both have codes
   * greater than {@code '\u005Cu0020'} (the space character), then a
   * reference to this {@code String} object is returned.
   * <p>
   * Otherwise, if there is no character with a code greater than
   * {@code '\u005Cu0020'} in the string, then a
   * {@code String} object representing an empty string is
   * returned.
   * <p>
   * Otherwise, let <i>k</i> be the index of the first character in the
   * string whose code is greater than {@code '\u005Cu0020'}, and let
   * <i>m</i> be the index of the last character in the string whose code
   * is greater than {@code '\u005Cu0020'}. A {@code String}
   * object is returned, representing the substring of this string that
   * begins with the character at index <i>k</i> and ends with the
   * character at index <i>m</i>-that is, the result of
   * {@code this.substring(k, m + 1)}.
   * <p>
   * This method may be used to trim whitespace (as defined above) from
   * the beginning and end of a string.
   *
   * @return A string whose value is this string, with any leading and trailing white space removed,
   * or this string if it has no leading or trailing white space.
   */
  public String trim() {
    int len = value.length;
    int st = 0;
    char[] val = value;    /* avoid getfield opcode */

    while ((st < len) && (val[st] <= ' ')) {
      st++;
    }
    while ((st < len) && (val[len - 1] <= ' ')) {
      len--;
    }
    return ((st > 0) || (len < value.length)) ? substring(st, len) : this;
  }

  /**
   * This object (which is already a string!) is itself returned.
   *
   * @return the string itself.
   */
  public String toString() {
    return this;
  }

  /**
   * Converts this string to a new character array.
   *
   * @return a newly allocated character array whose length is the length of this string and whose
   * contents are initialized to contain the character sequence represented by this string.
   */
  public char[] toCharArray() {
    // Cannot use Arrays.copyOf because of class initialization order issues
    char result[] = new char[value.length];
    System.arraycopy(value, 0, result, 0, value.length);
    return result;
  }

  /**
   * Returns a formatted string using the specified format string and
   * arguments.
   *
   * <p> The locale always used is the one returned by {@link
   * java.util.Locale#getDefault() Locale.getDefault()}.
   *
   * @param format A <a href="../util/Formatter.html#syntax">format string</a>
   * @param args Arguments referenced by the format specifiers in the format string.  If there are
   * more arguments than format specifiers, the extra arguments are ignored.  The number of
   * arguments is variable and may be zero.  The maximum number of arguments is limited by the
   * maximum dimension of a Java array as defined by <cite>The Java&trade; Virtual Machine
   * Specification</cite>. The behaviour on a {@code null} argument depends on the <a
   * href="../util/Formatter.html#syntax">conversion</a>.
   * @return A formatted string
   * @throws java.util.IllegalFormatException If a format string contains an illegal syntax, a
   * format specifier that is incompatible with the given arguments, insufficient arguments given
   * the format string, or other illegal conditions.  For specification of all possible formatting
   * errors, see the <a href="../util/Formatter.html#detail">Details</a> section of the formatter
   * class specification.
   * @see java.util.Formatter
   * @since 1.5
   */
  public static String format(String format, Object... args) {
    return new Formatter().format(format, args).toString();
  }

  /**
   * Returns a formatted string using the specified locale, format string,
   * and arguments.
   *
   * @param l The {@linkplain java.util.Locale locale} to apply during formatting.  If {@code l} is
   * {@code null} then no localization is applied.
   * @param format A <a href="../util/Formatter.html#syntax">format string</a>
   * @param args Arguments referenced by the format specifiers in the format string.  If there are
   * more arguments than format specifiers, the extra arguments are ignored.  The number of
   * arguments is variable and may be zero.  The maximum number of arguments is limited by the
   * maximum dimension of a Java array as defined by <cite>The Java&trade; Virtual Machine
   * Specification</cite>. The behaviour on a {@code null} argument depends on the <a
   * href="../util/Formatter.html#syntax">conversion</a>.
   * @return A formatted string
   * @throws java.util.IllegalFormatException If a format string contains an illegal syntax, a
   * format specifier that is incompatible with the given arguments, insufficient arguments given
   * the format string, or other illegal conditions.  For specification of all possible formatting
   * errors, see the <a href="../util/Formatter.html#detail">Details</a> section of the formatter
   * class specification
   * @see java.util.Formatter
   * @since 1.5
   */
  public static String format(Locale l, String format, Object... args) {
    return new Formatter(l).format(format, args).toString();
  }

  /**
   * Returns the string representation of the {@code Object} argument.
   *
   * @param obj an {@code Object}.
   * @return if the argument is {@code null}, then a string equal to {@code "null"}; otherwise, the
   * value of {@code obj.toString()} is returned.
   * @see java.lang.Object#toString()
   */
  public static String valueOf(Object obj) {
    return (obj == null) ? "null" : obj.toString();
  }

  /**
   * Returns the string representation of the {@code char} array
   * argument. The contents of the character array are copied; subsequent
   * modification of the character array does not affect the returned
   * string.
   *
   * @param data the character array.
   * @return a {@code String} that contains the characters of the character array.
   */
  public static String valueOf(char data[]) {
    return new String(data);
  }

  /**
   * Returns the string representation of a specific subarray of the
   * {@code char} array argument.
   * <p>
   * The {@code offset} argument is the index of the first
   * character of the subarray. The {@code count} argument
   * specifies the length of the subarray. The contents of the subarray
   * are copied; subsequent modification of the character array does not
   * affect the returned string.
   *
   * @param data the character array.
   * @param offset initial offset of the subarray.
   * @param count length of the subarray.
   * @return a {@code String} that contains the characters of the specified subarray of the
   * character array.
   * @throws IndexOutOfBoundsException if {@code offset} is negative, or {@code count} is negative,
   * or {@code offset+count} is larger than {@code data.length}.
   */
  public static String valueOf(char data[], int offset, int count) {
    return new String(data, offset, count);
  }

  /**
   * Equivalent to {@link #valueOf(char[], int, int)}.
   *
   * @param data the character array.
   * @param offset initial offset of the subarray.
   * @param count length of the subarray.
   * @return a {@code String} that contains the characters of the specified subarray of the
   * character array.
   * @throws IndexOutOfBoundsException if {@code offset} is negative, or {@code count} is negative,
   * or {@code offset+count} is larger than {@code data.length}.
   */
  public static String copyValueOf(char data[], int offset, int count) {
    return new String(data, offset, count);
  }

  /**
   * Equivalent to {@link #valueOf(char[])}.
   *
   * @param data the character array.
   * @return a {@code String} that contains the characters of the character array.
   */
  public static String copyValueOf(char data[]) {
    return new String(data);
  }

  /**
   * Returns the string representation of the {@code boolean} argument.
   *
   * @param b a {@code boolean}.
   * @return if the argument is {@code true}, a string equal to {@code "true"} is returned;
   * otherwise, a string equal to {@code "false"} is returned.
   */
  public static String valueOf(boolean b) {
    return b ? "true" : "false";
  }

  /**
   * Returns the string representation of the {@code char}
   * argument.
   *
   * @param c a {@code char}.
   * @return a string of length {@code 1} containing as its single character the argument {@code c}.
   */
  public static String valueOf(char c) {
    char data[] = {c};
    return new String(data, true);
  }

  /**
   * Returns the string representation of the {@code int} argument.
   * <p>
   * The representation is exactly the one returned by the
   * {@code Integer.toString} method of one argument.
   *
   * @param i an {@code int}.
   * @return a string representation of the {@code int} argument.
   * @see java.lang.Integer#toString(int, int)
   */
  public static String valueOf(int i) {
    return Integer.toString(i);
  }

  /**
   * Returns the string representation of the {@code long} argument.
   * <p>
   * The representation is exactly the one returned by the
   * {@code Long.toString} method of one argument.
   *
   * @param l a {@code long}.
   * @return a string representation of the {@code long} argument.
   * @see java.lang.Long#toString(long)
   */
  public static String valueOf(long l) {
    return Long.toString(l);
  }

  /**
   * Returns the string representation of the {@code float} argument.
   * <p>
   * The representation is exactly the one returned by the
   * {@code Float.toString} method of one argument.
   *
   * @param f a {@code float}.
   * @return a string representation of the {@code float} argument.
   * @see java.lang.Float#toString(float)
   */
  public static String valueOf(float f) {
    return Float.toString(f);
  }

  /**
   * Returns the string representation of the {@code double} argument.
   * <p>
   * The representation is exactly the one returned by the
   * {@code Double.toString} method of one argument.
   *
   * @param d a {@code double}.
   * @return a  string representation of the {@code double} argument.
   * @see java.lang.Double#toString(double)
   */
  public static String valueOf(double d) {
    return Double.toString(d);
  }

  /**
   * Returns a canonical representation for the string object.
   * <p>
   * A pool of strings, initially empty, is maintained privately by the
   * class {@code String}.
   * <p>
   * When the intern method is invoked, if the pool already contains a
   * string equal to this {@code String} object as determined by
   * the {@link #equals(Object)} method, then the string from the pool is
   * returned. Otherwise, this {@code String} object is added to the
   * pool and a reference to this {@code String} object is returned.
   * <p>
   * It follows that for any two strings {@code s} and {@code t},
   * {@code s.intern() == t.intern()} is {@code true}
   * if and only if {@code s.equals(t)} is {@code true}.
   * <p>
   * All literal strings and string-valued constant expressions are
   * interned. String literals are defined in section 3.10.5 of the
   * <cite>The Java&trade; Language Specification</cite>.
   *
   * @return a string that has the same contents as this string, but is guaranteed to be from a pool
   * of unique strings.
   */
  public native String intern();
}
